There are many instances in the recording field where it is desirable to apply a recording material to a recording medium such that the recording material contacts the medium with constant pressure even though the recording material is expended during the recording process. It is desirable that the contact between the recording material and medium be selectively interrupted so that the recording device may pass over areas of the recording medium where no recording or marking is to take place.
The prior art discloses many devices that teach techniques for obtaining the above desired operation. These prior art techniques vary depending on the recording material used. Where the recording material is a pencil lead various mechanical techniques have been used including mechanisms for chucking the lead and then feeding the lead under spring tension or using a special chucking mechanism with a screw arrangement or motor to feed the lead.
In the facsimile field where the recording material is an electronic stylus, similar problems occur as the tip of the stylus wears and must be fed at a constant pressure to obtain long life. In that application similar techniques have been used such as spring tension to maintain constant pressure contact. These techniques suffer from mechanical complexity and other disadvantages. If spring tension is used to maintain constant pressure contact then either the throw of the spring must be limited or the spring tension must be released when it is desirable to remove contact with the recording medium. In addition, where it is desired to have a long travel of the recording material, such as when using lead which wears rapidly, springs have a limited travel length for a constant pressure application. Where mechanical means are used to advance the lead such as a screw-motor arrangement, a major disadvantage is that only one lead may be placed in the mechanism at a time. The thin leads used in automatic drawing applications wear at an extremely high rate, and the number of feet of drawn line is limited especially when softer leads are used.
Accordingly, one object of the present invention is to provide an apparatus which allows for long periods of unattended operation and that accommodates multiple pieces of lead. The apparatus of the present invention automatically changes to a new lead as the previous lead is expended.
Another object of the present invention is to provide an apparatus and method for feeding a recording material onto a recording medium under constant pressure.
A further object of the present invention is to provide means for selectively removing contact between the recording material and medium. This object is performed in accordance with the present invention without undue mechanical complexity.
Another object of the present invention is to provide an apparatus for feeding pencil lead that permits the use of a plurality of pieces of lead to thereby provide long unattended operation.